Tension patch



P. H. KEMMER ET AL Oct. 26, 1948.

TENSION PATQH 2 Sheets-Sheet l Filed Jan. 17, 1946 Oct. 26, 1948. P. H.KEMMER ET AL TENSION PATCH 2 Sheets-Sheet 2 Filed Jan. 17, 1946 patentedOlivet. 26, 1948 WED STME onirica (Granted under" the' act ofi` March3.1883",I as

amended Aplil',V 1928; 370 G. 757)."

v Claims.

The invention described h'ereinfmayf be" manu'- factured and used by orfor'the Government for' governmental purposes without thepayrnentf to`us of any royalty thereon'.

This invention relates toa tensiclmi patch for static testing ofairfoil's; canopies, k'iub'bl'e's, blisters and radomes (i. e., radardomes) of aircraft, especially' military aircraft. Various method-s oftesting' the strength of aircraft wingsla-nd" similar structures havebeen proposed. For instance, the Cf; F. Bee'dPat'ent No. 2,340,505 datedleebrua-rvv l, 1944, discloses aerofoil testi-hg apparatus comprising a'series of sponge rubber layerssecured by' an adhesive tothe upper andlowersurfaces ofv` an airplane wing', with-a series of wood blockssecured to' the' sponge rubber' and" held in a frame which' surrounds'the wing" and is acted uponby adjustable forces whereby tensionI may beapplied to' the sponge rubbery layers on the upper face ofv the wing"andv compression may be simultaneously applied to the sponge' rubberlayers attached to' theunderside of the Wing". However,v tlief .framesare spaced' apart spanwis'e" of the wings, so that the' forces imposedon' a wing are not continuous as in actual flight, and' furthermore theframe-s areso made thatV canopies, bubbles;y blisters and iradon'i'escannot be tested.

This invention airns' to' provide improved appa-yra'tus-for'testing'surfacesof'an aircraft for 'burst-- ing streng-thy`so that portions of the; air-craft lmay be'y subjected' to substantiallythe `saine loads to whicli'th'ey would besubjected while' actual night.A particularfobject is to provide ai tension patch which' is equallystressed: throughout' its area evenrtho'ugh appliedto curved surfaces',the result being that there a're no overloadedf portions which arelikely to fail', compelling repetition ofv the test with `seriousimpairment of laboratory procedure: Another object is-to provideatension patch whichiis somade as'to-obviate'the'entrapment o-fany airbetween the cemented surfaces' of the tensioni patch' and the'objectflunder test. Further objects will bei'understoodibyreferring tothe' following descripti'onofeiribodi-rn'ents of the invention' inconnectionv withvthe' accompanying drawings forming part of thisspecification'.

In-the drawings:

Fig.'- l' is a' diagrarnitfiatic` sectional elevation' showing part of afuselage with' a' sliding' canopy under a static test,only'partoffthetestingappa# ratusbeingi' shown for simplicity ofillustration;

Fi'g.` 2`is1 a perspective View oflone for-m of. a` compoundcurvedtension patchrsuch as may be usedinle, test like that of Fig.v y11,;perforationsv being indicated in the patch to obviate the en# trapinentof' air under its nether' surface;

Fig. 3 isa pressure diagram of part of the fuse-'- lage of Fig. 1`,showing different' pressures on the' sliding canopy' at moderate airspeeds by I'neans of vectors, which arenot necessarily to scale;

Fig. 4 is a pressure' dia-gramof the sarne fuse` lage and canopy showninside elevation, various pressure curves being shown for differentsections; and

Figs. 5 to 8v inclusive are views in' side elevation showing fourdifferent fo'rns' of tension patchesapplied to a surface undertest.

Referring to the drawingsZ and rst' toFig'si 3 and 4, part of a fuselagel0 is shown having `a canopy H with a sliding section |25. Above thethrust line TQL the canopy whenv traveling' through the air at moderatespeed; lsay 20G-250 M. P; H., is subjected te pors'tingpressure duetjothe'negative pressure of lift, asshow'nl by the out-m wardly directedvectorsrVl. Below the thrust lineL T-L, the canopy' is subjected to;compression, as-

indicated by the inwardly directed vectors V2? As viewed` froinf theside; the'top-pafrt of the canopy sustains' the' greatest-'burstingpressure' approximately in the" plane of 'line A', aridith-is pressurerapidly drops to`zeroforwardly'ofplane ALA' anu-"becomes a compressionwhose` vaiue is' nearly es great-in the plane of line at 'the' frontpart of the canopy asfis 'the' absoluteval'ue of the bursting pressurein the piane Aa g Similar curves-P2 an'd`P3 are also shown for prese'change in' shap'eof th'ec'anop'y will n'ia'kemarked" differences in the"shapes: (if the pressr'e curves@ at all speeds: AfIsirnil'a'r'family'o'f c'ii'wescolillbeA Shown' fora larlgenuhiber ofblisters', adrn'esi' bubble-s and airfoils whic'hhave been tested inWind tunnels at varois" air speeds;A The fore* going will make it clearthat thel sta'tic testing of! many parts of ani airpla'i'ie' is 'a`highlyfco'inplex business since there f aref large pressure' diiereti'etials at' points only'a fewA inches' apart;

In accordance' with theI i'nver'it'ib'ng we provide tension patches"consisting o'f aiy layerf or bodyioi'l" synthetic' rubber' or similar'm`aterial,\ beingi rela-'e tively soft, backed by a base plate which isof relatively hard material, being preferably of metal, the base platebeing secured by an adhesive to the rubber body and having couplingmeans by which a load may be applied to the tension patch, Whoseunderside is cemented to the surface under test. Instead of syntheticrubber for the body of the patch we may employ wool or other hairy hideor cotton fabric as disclosed in our Patent No. 2,358,369, datedSeptember 19, 1944. Reference should also be made to our Patent No.2,383,491, dated August 28, 1945.

In the form of the invention shown in Fig. 2, a tension patch I4 ofcompound curvature is shown, consisting of a rubber body I5 whoseunderside is curved on two axes to nt perfectly the compound curvatureof a radoma canopy, blister, etc., to which it may be secured by theproper type of cement such as EC6l3 lsold by Minnesota Mining 8iManufacturing Company, St. Paul, Minnesota. The rubber body I5 iscemented toa metal base plate I6 to the center of which a stirrup Il iswelded. A clevis I8 is linked with stirrup Il and a wire rope or cableI9 is secured to clevis I8 and transmits the load 23, as shown in Fig.1, which may be one or more sandbags, or in some cases hydrauliccylinders r the like may be employed. It will be observed that thecentroid C of the cemented area is directly beneath the line of tensionof rope I3, so that the entire area of the rubber body I is evenlyloaded. If the line of tension, prolonged, does not contain centroid C,then there will be underloaded areas and overloaded areas, and theoverload may be sufficient to cause the adhesive layer or the rubberbody to give Way, with the result that the entire test `must berepeated. Another feature is the provision of a considerable number ofperforation-s 2l which are provided both in the metal base plate I6 andin the rubber or other body I5, tomake it impossible to entrap airbetween the surface to be testedand the netheior cemented side of thetension patch.

Referring again to Fig. l, it may be assumed that canopy II is beingtested with the aid of a considerable number of tension patches I4 likethe one shown in Fig. 2. Each patch I4 has a wire rope I8 attachedthereto, and all such ropes pass over properly positioned pulleys 22(only three being shown) and support loads 23 of various weightscalculated to impose theproper tension on the corresponding tensionpatches. Pulleys 22 are carried on an open steel frame 23 made ofI-beams and: other standard shapes, which normally enclosesthe objectunder test, while permitting personnel of the laboratory to have freeaccess to the object to place and remove the tension patches. Frame 23may be portable so that it may be moved about on the door of thelaboratory, or it may be fixed to a wall of the building.

While tension patches I4 are perfectly satisfactory if the lines oftension of the ropes I9 ex tend in the proper direction; however, shouldthe ropes not be supported properly to bring the centroid of the tensionpatch in the line of tension, then each tension patch Will have an areaof low tension and other areas which are overloaded, as previouslystated.

In Figs. -58, We show four different forms of tension patches each ofwhich has means interposed between its rope and the base plate andacting automaticallyito make the line of tension always include thecentroid. Each of these four modifications may -have perforations like'perforations 2 I, Fig. 2, although the same are not shown.

In the form of Fig. 5, the tension patch 24 includes a base plate 25 anda pair of clevises 26, 2l of unequal length, each clevis 26, 21 beinghinged at one end to the base plate by means of straps 28 secured tosaid plate andproviding eyes, each clevis being pivotally connected atthe other end by pins 29 to a straight bar 30. This bar 30 has alongitudinally extending rowfof perforations 3| for a clevis pin 32 bywhich clevis 33 may be secured to the barat a selected point. Rope I9 issecured to the clevis 33 and is trained over a pulley as previouslyexplained. If clevis pin 32 is properly positioned on bar 3B, the lineof tension of rope I9 will pass through the centroid C.

In the form of Fig. 6, the tension patch 34 includes a base plate 35which has an arcuate plate or bar 36 secured thereto, said arcuate platehaving a plurality of arcuately arranged perforations 31 for receiving aclevis pin 38 of a olevis 39fwhereby the rope I9 is anchored to thetension patch. By properly selecting the position of clevis pin 38, theline of tension may be made to pass through the centroid C.

In the form of Fig. 7, the tension patch 44 includes a base plate 45which has an arcuate rod or stirrup 45 welded thereto, and a clevis 41,which is anchored to the end of rope I8, carries a grooved sheave 48which may travel along the arcuate rod to automatically line up thecable with the centroid C.

In the form of Fig. 8, the tension patch 54 includes a base plate 55which has a short wire cable 56 secured at both ends by cable anchors 51in the eyes in blocks 53 secured to the base plate. Cable 55 is longerthan the distance between blocks 58, and its anchors 57 may be pivotedinthe blocks. Y A clevis 59, which is secured to the end of rope I9,carries a grooved sheave 60 which travels over yWire cable 56 to causerope I9 to line up automatically with the centroid C.

The four forms of tension patch shown in Figs. 5-8 inclusive arecharacterized by the application of the line of force through thecentroid of the cemented area, either by adjustment of the rope couplingdevice or by automatic adjustment caused by the construction of thecoupling device. The result is an evenly distributed tension over theentire cemented area and there are consequently no overloaded areas. Thebars 3D, 36 and 45 of Figs. 5, 6 and 7 and the cable 56 of Fig. 8 may betermed load distributing members, since they are attached at oppositeend portions to the base plates of the tension patches illustrated andthus act to distribute the load more evenly'across the tension patchstructure.

Having described our invention, what we claim as new and desire tosecure by Letters Patent is:

l. A tension patch for load testing of aircraft comprising, a relativelysoft sheet member adapted to be cemented throughout one side to aportion of the outer surface of an aircraft structure under test, arelatively hard base plate having the same size and outline as saidsheet member and rmly secured thereto in contiguous face-to-facerelation, load attaching means including a load distributing memberextending across said base plate and having opposite end portionssecured thereto, a tension cable attaching means connected to said loaddistributing member at a point between its opposite end portions, meansalong the length of said load distributing member, between said endportions, providing for adjustment of said cable attaching means withrespect to said opposite end portions of said load distributing memberin order to connect said tension cable attaching means at a selectedpoint along said load distributing member such that the line of thetension force exerted by the tension cable will intersect the centroidof the cemented area of said sheet member. I

2. A tension patch for load testing of aircraft comprising, a relativelysoft sheet member adapted to be cemented throughout one side to aportion of the outer surface of an aircraft structure under test, arelatively hardv base plate having the same size and outline as saidsheet member and firmly secured thereto in contiguous faceto-facerelation, load attaching means including a rigid bar extending acrosssaid base plate and having opposite end portions secured thereto, atension cable attaching means connected to said bar at a point betweenits opposite end portions, means along the length of said bar, betweensaid end portions, providing for adjustment of said cable attachingmeans with respect to said opposite end portions of said bar in order toconnect said tension cable attaching means at a selected point alongsaid bar such that the line of the tension force exerted by the tensioncable will intersect the centroid of the cemented area of said sheetmember.

3. A tension patch for load testing of aircraft comprising, a relativelysoft sheet member adapted to be cemented throughout one side to aportion of the outer surface of an aircraft structure under test, arelatively hard base plate having the same size and outline as saidsheet member and firmly secured thereto in contiguous face-to-facerelation, said sheet member and base plate being pierced by amultiplicity of perforations which extend from the cemented surface ofsaid sheet member to the outer face of the base plate to provide for theescape of air which may be entrapped between the sheet member and theouter surface of the structure under test, load attaching meansincluding a rigid bar extending across said base plate and havingopposite end portions secured thereto, a tension cable attaching meansconnected to said bar at a point between its opposite end portions,means along the length of said bar, between said end portions, providingfor adjustment of said cable attaching means with respect to saidopposite end portions of said bar in order to connect said tension cableattaching means at a selected point along said bar such that the line ofthe tension force exerted by the tension cable will intersect thecentroid of the cemented area of said sheet member.

4. A tension patch for load testing of aircraft comprising, a relativelysoft sheet member adapted to be cemented throughout one side to aportion of the outer surface of an aircraft structure under test, arelatively hard base plate having the same size and outline as saidsheet member and firmly secured thereto in contiguous face-to-facerelation, load attaching means including a rigid bar extending acrosssaid base plate and having opposite end portions secured thereto, atension cable attaching means including an element passing through anyone of a series of perforations in said bar extending longitudinallythereof in order to connect said tension cable attaching means to saidbar at a selected point therealong such that the line of the tensionforce exerted by the tension cable will intersect the centroid of thecemented area of said sheet member.

5. A tension patch for load testing of aircraft comprising, a relativelysoft sheet member adapted to be cemented throughout one side to aportion of the outer surface of an aircraft structure under test, arelatively hard base plate having the same size and outline as saidsheet member and firmly secured thereto in contiguous face-to-facerelation, load attaching means including an outwardly curved rigid barextending across said base plate and having opposite end portionssecured thereto, a tension cable attaching means including a sheaveadapted to roll on said curved bar and a cable attaching clevis havingsaid sheave rotatably mounted thereon, the application of tension to thecable attached to said clevis being adapted to automatically adjust theposition of said sheave along said curved bar to a point such that theline of the tension force exerted by the tension cable will intersectthe centroid of the cemented area of said sheet member.

PAUL H. KEMMER. EDGAR R. WEAVER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,159,667 Haley Nov. 9, 19151,852,758 Schroeder Apr. 5, 1932 2,048,144 Showers, Jr July 21, 19362,319,675 Grinter May 18, 1943 2,358,369 Weaver et al Sept. 19, 19442,404,602 Stoiilet July 23, 1946 FOREIGN PATENTS 5 Number Country Date39,422 Norway Aug. 4, 1924 440,656 Great Britain Jan. 3, 1936

